1. Field of the Invention
The present invention relates to a powder pressing apparatus and a powder pressing method. More specifically, the present invention relates to a powder pressing apparatus and a powder pressing method for manufacture of a compact to be made into a Rxe2x80x94Fexe2x80x94B magnet.
2. Description of the Related Art
FIG. 12 shows a primary portion of a powder pressing apparatus 1 for pressing a powder into a compact. According to the powder pressing apparatus 1, hollow cylindrical compacts each having, for example, a height of 6.4 mm, an inner diameter of 1.8 mm and an outer diameter of 4 mm are formed.
Now, an operation of the powder pressing apparatus 1 will be described briefly.
First, a die 2 is raised to a predetermined position, whereupon a feeder box 3 is moved above the die 2, allowing the powder contained in the feeder box 3 to fall into cavities 4 of the die 2. The feeder box 3 is then withdrawn, with its lower edge wiping the powder. Thereafter, an upper punch (no illustrated) is lowered to press the powder into compacts in the cavities 4. Then, the upper punch is raised whereas the die 2 is lowered, so that the compacts are out of the die. The compacts are then pushed by a front face 3a of the feeder box 3, and slid on the die 2 and a base plate 5 off pressing area.
Since the compacts are soft, pushing by the feeder box 3 is a desirable method of taking out small compacts after the compacting. However, if a number of compacts are pushed as shown in FIG. 12, in a direction of the row of compacts, then the compacts can hit thereby chipping or breaking each other, and the probability increases with the number of compacts in the row. This has limited the number of compacts which can be formed per press, and has been a cause of low productivity.
Alternatively, the compact can be taken out by a robot which is movable in the sliding direction of the feeder box 3. However, it is very difficult for the robot to grasp the small and fragile compact, in a short handling time such as a second or two.
The problem is even more serious in a compact used in manufacture of a Ndxe2x80x94Fexe2x80x94B magnet, in which the compact is very soft and even more difficult to handle, because the compact is made into a low density for the sake of magnetic property, and a lubricant is added for improved orientation.
It is therefore an object of the present invention to provide a powder pressing apparatus and a powder pressing method capable of improving yield and productivity.
According to an aspect of the present invention, there is provided a powder pressing apparatus which presses a powder into compacts in a plurality of cavities formed in a die, comprising: powder supply means which supplies the powder into the cavities; orienting means which orients the powder in the cavities; pressing means which presses the powder in the cavities into the compacts; and pushing means which pushes the compacts off the die; wherein none of the cavities overlap with another in a direction of pushing the compacts.
According to another aspect of the present invention, there is provided a powder pressing method for pressing a powder into compacts in a plurality of cavities formed in a die, comprising: a step of supplying the powder into the cavities; a step of orienting the powder in the cavities; a step of pressing the powder in the cavities into the compacts; and a step of pushing the compacts off the die, without allowing any of the compacts to contact another.
In this invention, none of the cavities overlap with another, in the pushing direction of the compacts. Therefore, each of the compacts can be taken out without making contact with another. Thus, yield is improved and productivity can be increased. Even if the compacts are oriented, taking can be performed favorably.
According to still another aspect of the present invention, there is provided a powder pressing apparatus which presses a powder into a compact in a cavity formed in a die, comprising: powder supply means which supplies the powder into the cavity; orienting means which orients the powder in the cavity; pressing means which presses the powder in the cavity into the compact; and pushing means which pushes the compact off the die; wherein the pushing means is provided by a flexible and elastic member.
According to still another aspect of the present invention, there is provided a powder pressing method for pressing a powder into a compact in a cavity formed in a die, comprising: a step of supplying the powder into the cavity; a step of orienting the powder in the cavity; a step of pressing the powder in the cavity into the compact; and a step of pushing the compact off the die, by using a flexible member.
In this invention, since the compact is pushed by the flexible member, pushing force can be applied gradually, instead of all at once, to the compact at the time of pushing. Therefore, even the soft compact can be pushed successfully, without being broken or tipped over.
According to still another aspect of the present invention, there is provided a powder pressing apparatus which presses a powder into a compact in a cavity formed in a die, comprising: powder supply means which supplies the powder into the cavity; orienting means which orients the powder in the cavity; pressing means which presses the powder in the cavity into the compact; pushing means which pushes the compact off the die; and an anti-wear layer provided in a region where the compact pushed by the pushing means slides.
According to still another aspect of the present invention, there is provided a powder pressing method for pressing a powder into a compact in a cavity formed in a die, comprising: a step of supplying the powder into the cavity; a step of orienting the powder in the cavity; a step of pressing the powder in the cavity into the compact; and a step of pushing thereby sliding the compact off the die, on an anti-ware layer.
In this invention, when being pushed, the compact is slid on the anti-wear layer that has a small surface roughness. Therefore, friction force associating with the sliding compact can be reduced, and the compact can be pushed without being broken.
According to still another aspect of the present invention, there is provided a powder pressing apparatus which presses a powder into a compact in a cavity formed in a die, comprising: powder supply means which supplies the powder into the cavity; orienting means which orients the powder in the cavity; pressing means which presses the powder in the cavity into the compact; and pushing means which pushes the compact off the die; and applying means which applies a die lubricant to the die (through-hole) but not to a region where the compact slides.
According to still another aspect of the present invention, there is provided a powder pressing method for pressing a powder into a compact in a cavity formed in a die, comprising: a step of applying a die lubricant to the die but not to a region where the compact slides; a step of supplying the powder into the cavity; a step of orienting the powder in the cavity; a step of pressing the powder in the cavity into the compact; and a step of pushing the compact off the die.
In this invention, since the die lubricant is not applied to the region where the compact is slid, the pushing operation of the compact is not influenced by the die lubricant, and can be performed smoothly.
According to still another aspect of the present invention, there is provided a powder pressing apparatus which presses a powder into a compact in a cavity formed in a die, comprising: powder supply means which supplies the powder into the cavity; orienting means which orients the powder in the cavity, including a pair of yokes sandwiching the die; pressing means which presses the powder in the cavity into the compact; demagnetizing means which demagnetizes the compact and the yokes; and pushing means which pushes the compact off the die.
According to still another aspect of the present invention, there is provided a powder pressing method for pressing a powder into a compact in a cavity formed in a die, comprising: a step of supplying the powder into the cavity; a step of orienting the powder in the cavity by using a pair of yokes sandwiching the die; a step of pressing the powder in the cavity into the compact; a step of demagnetizing the compact and the yokes; and a step of pushing the compact off the die.
In this invention, since the obtained compact and the yokes are demagnetized after the compacting of the powder, the compact can be smoothly slid on the die.
According to still another aspect of the present invention, there is provided a powder pressing apparatus which presses a powder into a compact in a cavity formed in a die, comprising: pressing means which presses the powder in the cavity into the compact; and orienting means which orients the powder in the cavity, including a pair of yokes sandwiching the die; wherein the die and the yokes each has an upper surface generally in a same plane.
In this invention, by forming the upper surfaces of the yokes and the die flush with each other, the orienting means does not interfere with the powder supplying means, thereby increasing freedom in disposition and movement of the powder supplying means. Further, the powder in an upper portion of the cavity can be reliably oriented.
Preferably, the pushing means is provided in the powder supplying means. This arrangement allows to integrate the pushing means with the powder supplying means, into a simple construction. Further, the operations of taking out the compact and supplying the powder into the cavity can be performed almost simultaneously, and operation action can be simplified.
Further, preferably, a feeder box containing the powder therein and having a front portion formed with a pushing means is used, the feeder box is moved on the die for supplying the powder contained in the feeder box into the cavity, while allowing the pushing means to push the compacts off the die. With this arrangement, the powder can be supplied into the cavity while pushing the compact. Therefore, time necessary for a cycle of the pressing operation can be shortened and productivity can be improved.
Further, preferably, the cavities are formed generally in line in a direction generally perpendicular to an orienting direction. With this arrangement, powder in each of the cavities can be oriented in the direction perpendicular to the row of cavities. This makes possible to uniformly magnetize all of the compacts to have the same magnetic characteristic. By sintering these compacts, sintered bodies of a uniform, desired shape can be obtained.
According to this invention, even if the compact to be taken out by sliding is made of a rare-earth alloy powder and therefore is highly fragile, it is possible to prevent damage of the compact and to improve yield.
Also, according to this invention, even if the rare-earth alloy powder is mixed with a lubricant, and therefore the compact is even softer and more susceptible to damage, the present invention is effective since it is possible to prevent damage to the compact.
Compacts made from a rare-earth alloy powder have a small density in order to attain a predetermined level of orientation. According to the present invention, even if the density is low, not smaller than 3.9 g/cm3 and not greater than 4.6 g/cm3, and the compact is highly susceptible to damage, the present invention is effective since it is possible to prevent damage of the compact.
According to the present invention, even if the compact is formed into a hollow member, which is highly fragile and difficult for a robot to grasp for example, the present invention is more effective since it is possible to prevent damage to the compact.
If a magnet obtained by sintering the hollow compact as described above is used in a motor, and the magnet is rotated as a rotor, the magnet is subjected to a very strong force. However, according to the present invention, the magnet has a high quality, and therefore can stabilize the quality of motor.
The above objects, other objects, characteristics, aspects and advantages of the present invention will become clearer from the following description of embodiments to be presented with reference to the accompanying drawings.